BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to laser ablatable hydrophobic fluorine-containing graft copolymers, and more in particular to articles such as ink jet printheads that are coated with a hydrophobic fluorine-containing graft copolymer that is laser ablatable. The invention also relates to methods of making fluorine-containing polymers laser ablatable within a desired wavelength range, and to a method of making a laser ablated article that includes the fluorine-containing article of this invention.
2. Description of Related Art
Laser ablated nozzle plates of ink jet nozzles are known to provide excellent drop ejector performance. One example of an ink jet nozzle in which the openings therein are formed with a laser can be seen in U.S. Pat. No. 5,291,226, incorporated herein by reference in its entirety. This patent describes an inkjet printhead that includes a nozzle member formed of a polymer material that has been laser-ablated to form inkjet orifices, ink channels, and vaporization chambers in the unitary nozzle member. The nozzle member is then mounted to a substrate containing heating elements associated with each orifice. In a preferred method, the orifices, ink channels, and vaporization chambers are formed using an excimer laser.
In ink jet printing, a printhead is provided, the printhead having at least one ink-filled channel for communication with an ink supply chamber at one end of the ink-filled channel. An opposite end of the ink-filled channel has a nozzle opening from which droplets of ink are ejected onto a recording medium. In accordance with the ink droplet ejection, the printhead forms an image on the recording medium. The ink droplets are formed as ink forms a meniscus at each nozzle opening prior to being ejected from the printhead. After a droplet is ejected, additional ink surges to the nozzle opening to reform the meniscus.
The direction of the ink jet determines the accuracy of placement of the droplet on the receptor medium, which, in turn, determines the quality of printing performed by the printer. Accordingly, precise jet directionality is an important property of a high quality printhead. Precise jet directionality ensures that ink droplets will be placed precisely where desired on the printed document. Poor jet directionality results in the generation of deformed characters and visually objectionable banding in half tone pictorial images. Particularly with the newer generation of thermal ink jet printers having higher resolution enabling printing at at least 360 dots per inch, improved print quality is demanded by customers.
A major source of ink jet misdirection is associated with improper wetting of the front face of the printhead containing at least one nozzle opening. One factor which adversely affects jet directional accuracy is the accumulation of dirt and debris, including paper fibers, on the front face of the printhead. Another factor which adversely affects jet directional accuracy is the interaction of ink previously accumulated on the front face of the printhead with the exiting droplets. This accumulation is a direct consequence of the forces of surface tension, the accumulation becoming progressively severe with aging due to chemical degradation (including, for example, oxidation, hydrolysis, reduction (of fluorine), etc.) of the front face of the printhead. Ink may accumulate on the printhead front face due to either overflow during the refill surge of ink or the splatter of small droplets resulting from the process of ejecting droplets from the printhead. When accumulated ink on the front face of the printhead makes contact with ink in the channel (and in particular with the ink meniscus at the nozzle orifice), the meniscus distorts, resulting in an imbalance of forces acting on the ejected droplet. This distortion leads to ink jet misdirection. This wetting phenomenon becomes more troublesome after extensive use of the printhead as the front face either chemically degrades or becomes covered with dried ink film. As a result, gradual deterioration of the generated image quality occurs.
One way of avoiding these problems is to control the wetting characteristics of the printhead front face so that no accumulation of ink occurs on the front face even after extensive printing. Thus, in order to provide accurate ink jet directionality, wetting of the front face of the printhead is preferably suppressed. This can be achieved by rendering the printhead front face hydrophobic.
For example, U.S. Pat. No. 5,218,381, incorporated herein by reference in its entirety, describes a coating comprising an epoxy adhesive resin such as EPON 1001F, for example, doped with a silicone rubber compound such as RTV 732. The coating can be provided in the form of a 24% solution of EPON 1001F and a 30:70 mixture of xylene and methyl iso-butyl ketone by weight doped with 1% by weight of RTV 732. Such a coating enables the directionality of an ink jet to be maintained for the printing lifetime of the printer. An adhesion promoter such as a silane component, for example, can also be included to provide a highly adherent, long lasting coating.
While laser ablated nozzle plates are able to provide excellent drop ejector performance as discussed above, a practical problem in so forming the nozzle plates is that while polymer materials used for the nozzle plate, for example polyimides, are laser ablatable with lasers such as excimer lasers, such polymers are not hydrophobic. It is thus necessary to provide a hydrophobic coating upon the surface of the nozzle plate to render the front face hydrophobic to improve the ink jet accuracy as discussed above.
It is difficult to apply a coating to a face of an ink jet nozzle plate after formation of the openings therein. While it is desirable to suppress the wetting property of the nozzle surface, it is also undesirable to allow any coating material to enter the channel of the nozzle. If the walls of the channel become coated with ink-repellent material, proper refill of the channel may be inhibited. Refill of each channel depends on surface tension and must be completed in time for the subsequent volley of droplets to be fired. If the refill process is not completed by the time the next droplet is fired, the meniscus may not be flush with the outer edge of the nozzle opening, resulting in misdirection. Further, an incompletely filled channel causes the ink droplet size to vary, which also leads to print quality degradation.
Providing the front face of nozzle plates with a hydrophobic coating prior to formation of the openings is also problematic when attempting to form the openings by laser ablation. Hydrophobic coating materials in general, and fluorine-containing polymers more specifically, are not laser ablatable, i.e., they are transparent to radiation at the wavelengths of 210-360 nm such as generated by excimer lasers and the third and fourth harmonics of NdYAG lasers.
U.S. Pat. No. 4,915,981 describes a method of ablating fluoropolymer composite materials wherein it was found that small holes (less than 100 μm) can be formed in fluoropolymer composite laminate materials using UV lasers of wavelengths between 190 nm and 400 nm. The resulting holes can be used to produce vias and plated through-holes having smooth side walls with little or no debris or residue remaining in the holes and minimal damage to the polymer. Thus, the vias and plated through-holes can be plated without further cleaning processes. The fluoropolymeric composite is at least one of the fluoropolymers selected from the group consisting of polytetrafluoroethylene (PTFE), a copolymer of TFE and perfluorovinyl ether (PFA), a copolymer of TFE and hexafluoropropylene (FEP) and a polychlorotrifluoroethylene (PCTFE) that contains a filler that absorbs within the specified UV range, for example a filler of at least one of microglass, silica, titanium dioxide, carbon fibers, microballoons and Kevlar.
U.S. Pat. No. 5,169,678 discloses that the ultraviolet absorption characteristics of a polymer material are modified by the addition of an ultraviolet absorbing dye to render it laser ablatable at a frequency at which the unmodified material is substantially non-laser ablatable, desirably at a wavelength of 351 nm. A method of making a high density interconnect structure using the polymer material is detailed. The ultraviolet absorbing dye may be of several specific types, including, e.g., p-phenylazophenol, N-p-methoxybenzylidene-p-phenylazoaniline, dihydroxyanthraquinone, beta carotene, etc. having an absorption band which includes the selected ultraviolet wavelength.
While hydrophobic polymer materials have been made to absorb ultraviolet radiation so as to be laser ablatable with light from an ultraviolet laser, use of an ultraviolet laser to form the openings of a nozzle face plate is not ideal. Such lasers tend to be less economical and more cumbersome to use compared to, e.g., excimer lasers. Such laser operate deep in the ultraviolet light region, tend to form ozone from oxygen, and require more expensive optics.
What is still desired is an improved method of making laser ablatable articles such as nozzle face plates of ink jet printhead devices that contain a hydrophobic fluorine-containing polymer and which article is laser ablatable with a laser such as a KrF (krypton fluoride) or argon chloride (ArCl) excimer laser, or at the third or fourth harmonics of an NdYAG laser.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to make a fluorine-containing polymer that is laser ablatable by an excimer laser, for example laser ablatable within the wavelength range of from about 210 to about 360 nm, i.e., the near ultraviolet wavelength region.
It is a still further object of the present invention to derive an article that is hydrophobic or coated with a hydrophobic coating and that is laser ablatable with an excimer laser such that the article can be processed with the excimer laser.
It is a still further object of the present invention to achieve an economical and efficient method of processing an article that is hydrophobic, or coated with a hydrophobic coating, using an excimer laser.
These and other objects are achieved by the present invention, which in embodiments relates to a method of making a laser ablated article, comprising forming an article of one or more layers, wherein each of the layers absorbs radiation (light) output from a laser at wavelengths within the range of from about 210 nm to about 360 nm, and wherein at least one of the layers comprises a hydrophobic fluorine-containing graft copolymer derived from at least one fluorine-containing monomer and at least one comonomer containing at least one aromatic group, and processing the article with a laser that outputs radiation at a wavelength of between about 210 nm and about 360 nm. The invention also relates to a laser ablated article comprising one or more layers, wherein each of the layers absorbs radiation output from a laser within the wavelength range of from about 210 nm to about 360 nm, and wherein at least one of the layers comprises a hydrophobic fluorine-containing graft copolymer derived from at least one fluorine-containing monomer and at least one comonomer containing at least one aromatic group.
The invention also relates to an ink jet printhead comprising a nozzle plate, wherein the nozzle plate contains ink jet openings and comprises a polymer substrate coated with a laser ablatable hydrophobic coating comprised of a hydrophobic fluorine-containing graft copolymer derived from at least one fluorine-containing monomer and at least one comonomer containing at least one aromatic group, and wherein the laser ablatable hydrophobic coating is laser ablatable within the wavelength range of from about 210 nm to about 360 nm.